In the modern communication networks, with the development of data services, some real-time-critical services impose high requirements on frequency synchronization and time synchronization of the whole communication network. Frequency synchronization is a foundation of time synchronization. Without frequency synchronization, there is no precisely synchronous step of time or synchronized time.
The IEEE 1588 V2 protocol is a frequency time synchronization protocol, and is a precision clock synchronization protocol standard of the network measurement and control system, briefly known as Precision Time Protocol (PTP). The PTP aims to synchronize the distributed and independent clocks precisely.
As shown in FIG. 1, a time synchronization solution based on the PTP in the prior art is: All functions stipulated by the PTP, for example, timestamp processing, IEEE 1588 packet disassembling, clock time recovery, Best Master Clock (BMC) algorithm, and port state algorithm, are implemented by a dedicated core subsystem in a centralized way. The specific application port subsystems are responsible only for extracting IEEE 1588 packets, for example extracting an IEEE 1588 packet from a service packet, and inserting such packets, for example inserting an IEEE 1588 packet into a service packet. Only the relevant packets stipulated by the PTP are transmitted between an application port subsystem and a core subsystem.
In the foregoing solution, the timestamp processing is centralized in the core subsystem. The delay and jitters of packet transmission between the application port subsystem and the core subsystem may affect the precision of timestamp processing performed by the core subsystem.
Besides, in the foregoing solution, the core subsystem performs all functions stipulated by the PTP. With increase of the ports in the application port subsystems, the workload of the core subsystem may increase massively, thus affecting efficiency of frequency synchronization and time synchronization.
As shown in FIG. 2, another time synchronization solution based on the PTP in the prior art is: Each application port subsystem has complete IEEE 1588 protocol processing modules, including timestamp processing, IEEE 1588 V2 packet identification, extracting and inserting/assembling and disassembling, BMC algorithm and port state determining unit, and clock time recovering module, thus relieving the workload of the core subsystem and avoiding timestamp processing inaccuracy caused by delay and jitters of packet transmission.
However, because each application port subsystem contains complete IEEE 1588 protocol processing modules, the application port subsystems are independent of each other. At the time of selecting a clock source, only the best clock source in the application port subsystem can be selected, and it is impossible to select the best clock source in the whole system, thus affecting precision of frequency synchronization or time synchronization.